Molybdenum compounds of high purity are required for various applications such as in catalysts, etc.
Heretofore, there have been a number of processes for upgrading relatively impure molybdenum compounds as molybdenum trioxide.
U.S. Pat. No. 3,957,946 discloses a process for purifying molybdenum which involves subjecting impure concentrates of molybdenum trioxide to oxidative roasting, followed by ammoniacal leaching of the molybdic trioxide to produce ammonium molybdate which is further purified by passage through a chelating cation exchange resin.
U.S. Pat. Nos. 3,848,049 and 3,829,550 disclose purification processes for molybdenum which involve leaching of molybdenum trioxide with dilute nitric acid.
U.S. Pat. No. 3,694,147 discloses a process for purifying molybdenum trioxide of impurities such as lead, copper, iron, zinc and some alkaline earths by leaching with an aqueous solution of a hydrochloric acid and an ammonium salt of the halide.
U.S. Pat. No. 3,860,419 relates to the process for recovering molybdenum from molybdenum concentrates by digesting the concentrate in an aqueous nitric acid solution containing ammonium nitrate, separating the solid phase from the liquid phase, and treating the solid phase with ammonium hydroxide to produce ammonnium molybdate. In column 3 lines 9 to 16, the digesting solution is disclosed as containing substantially 1.0 to 4.0 moles per liter of free nitric acid and 0.5 to 2.0 moles per liter of ammonium nitrate. The weight ratio of solution to concentrate is substantially 1 to 1 to 3 to 1. In column 3, lines 17 to 26, the preferred range of the solution is described as containing from about 2.0 to 2.3 moles per liter nitric acid and 1.5 to 2 moles per liter of ammonium nitrate.
In the above processes some impurities remain to contaminate the product.
Potassium is a particularly difficult impurity to remove. When U.S. Pat. No. 3,860,419 is followed for purifying molybdenum, the potassium is not sufficiently reduced for use as high purity material.
Therefore, a process for purifying molybdenum in which the potassium from level is further reduced from the values given above be highly desirable and an advancement in the art.